Glass compositions and glass forming materials comprising said compositions

ABSTRACT

The present invention provides glass compositions that can be used instead of known glass compositions containing a large amount of PbO in applications such as coating ceramic substrates, e.g., alumina, or sealing fluorescent tubes or the like. The invention also provides glass forming materials containing the glass compositions as a primary component for glass formation. Glass compositions provided by the present invention are comprises essentially of primary oxide components. The primary oxide components include ZnO, B 2 O 3  and P 2 O 5  as essential components and Al 2 O 3 , MgO, CaO and BaO as optional components. The amount of the primary oxide components is 85 wt % or more (preferably 90 wt % or more) of the total weight of the glass composition. Typically, the primary oxide components include 45 to 80% of ZnO, 5 to 45% of B 2 O 3 , 1 to 35% of P 2 O 5 , 0 to 10% of Al 2 O 3 , 0 to 15% of MgO, 0 to 10% of CaO, and 0 to 5% of BaO.

TECHNICAL FIELD

The present invention relates to glass compositions (hereinafterreferred to “vitreous compositions”). More specifically, the presentinvention relates to glass compositions that can be used as coatings foralumina substrates or other inorganic materials, as sealants, as glaze(enamel) forming pastes and other glass forming materials containing theglass compositions as the primary component for glass formation.

BACKGROUND ART

Glass is used as a coating for ceramic substrates, such as alumina inwhich a circuit is formed on the surface, or as a sealant forfluorescent tubes and the like. Previously, glass compositionscontaining a large amount of lead oxide (hereinafter referred to as“high PbO glass compositions”) or glass forming materials (typically, apaste-like glaze forming material) containing such compositions as theprimary component were used as materials for forming glass in suchapplications. High PbO glass compositions have a low melting point, areeasily formed into glass by glass forming processing, and have superiorelectrical insulation properties, thereby making high PbO glasscompositions suitable for the above-described applications. For example,Japanese Laid-Open Patent Publication No. 62-207739 discloses a high PbOglass composition suitable for the above-described applications.

However, in recent years, so-called lead-free glass compositionscharacterized by containing substantially no lead oxide have been usedinstead of high PbO glass compositions, in view of increasing concernsabout preventing environmental pollution and to improve workplaceconditions. For example, Japanese Laid-Open Patent Publication Nos.7-81972, 8-183632, 9-188544 and 10-236845 disclose several types oflead-free glass compositions intended for use in the above-describedapplications.

However, the known lead-free glass compositions disclosed in theabove-noted publications do not have properties that are comparable tothe known high PbO glass composition with respect to the applications ofcoating and sealing. For example, the known lead-free glass compositionsgenerally have firing temperatures (typically about 900° C.) that arehigher than the high PbO glass compositions. If the surface of an object(e.g., a ceramic circuit board) is glass-coated with such a lead-freeglass composition, it is necessary to fire the object at a relativelyhigh temperature after the lead-free glass composition (typically aglaze forming material prepared in the form of paste) is applied to theobject. Therefore, the high temperature during firing may adverselyaffect the properties of the object.

It is an object of the present invention to provide glass compositionsthat can be used in applications such as coating ceramic substrates,e.g., alumina, or sealing fluorescent tubes or the like under the sameconditions that were used for the known high PbO glass compositions andwithout containing a large amount of lead (typically lead-free); glassforming materials containing such glass compositions as the primarycomponent for glass formation are also provided.

SUMMARY OF THE INVENTION

Glass compositions provided by the present invention comprise primaryoxide components in an amount of 85% (by weight, which applies to thefollowing discussion) or more (preferably 90% or more) of the totalweight of the composition; the primary oxide components include ZnO,B₂O₃ and P₂O₅ as essential components and the primary oxide componentsare provided in the amounts of 50 to 80% of ZnO, 5 to 35% of B₂O₃, 1 to20% of P₂O₅, 0 to 10% of Al₂O₃, 0 to 15% of MgO, 0 to 10% of CaO, and 0to 5% of BaO.

Additional glass compositions provided by the present invention includeglass compositions that are substantially free of lead oxide andcomprise primary oxide components in an amount of 90% or more(preferably 95% or more) of the total weight of the composition; theprimary oxide components include ZnO, B₂O₃ and P₂O₅ as essentialcomponents and the primary oxide components are provided in the amountsof 45 to 80% of ZnO (preferably, 45 to 75% of ZnO), 5 to 45% of B₂O₃, 1to 35% of P₂O₅, 0 to 10% of Al₂O₃, 0 to 15% of MgO, 0 to 10% of CaO, and0 to 5% of BaO.

Glass compositions having these formulations (e.g., oxide glasscompositions substantially comprising only vitreous oxide components) donot require excessive care to prevent environmental pollution, unlikethe high PbO glass compositions. Furthermore, the firing temperature canbe set to a temperature lower than known lead-free glass compositions(e.g., 650° C. or less). Therefore, it is possible to prevent propertydegradation of an object subjected to a glass coating process, such as aceramic substrate, due to high firing temperatures. Preferably, the sumof the weight percentages of Al₂O₃, MgO, CaO and BaO in the glasscompositions of the present invention is 15% or less (more preferably,10% or less) of the total weight of the primary oxide components.

Additional preferred glass compositions of the present inventioncomprise primary oxide components in the amounts of 50 to 65% of ZnO, 10to 30% of B₂O₃, and 10 to 30% of P₂O₅ (provided that the sum of theweight of B₂O₃ and P₂O₅ is 30 to 45% of the total weight of thecomposition); in addition, the glass compositions include 0 to 15% ofone or two or more oxides selected from the group consisting of Al₂O₃,MgO, CaO, and BaO (provided that the weight percentage of BaO is 0 to 5%of the total weight of the primary oxide components). Such glasscompositions can realize improved glass formation at comparatively lowfiring temperatures.

Another preferred glass composition of the present invention is an oxideglass composition that substantially comprises said primary oxidecomponents in any of said weight proportions (the presence of a traceamount of impurities on the order of less than 1% is allowable).

Other preferred glass compositions of the present invention aresubstantially free of SiO₂ or only include SiO₂ in an amount of lessthan 1% of the total weight of the composition. Glass compositions thatare free of SiO₂ or contain an extremely low amount of SiO₂ arepreferable, because such glass compositions rarely devitrify duringglass formation.

Other preferred glass compositions of the present invention aresubstantially free of alkali metal oxides and alkali metal ions (i.e.,these substances are not present at all, or if present, the amountthereof is only in an unavoidable level as impurities or in a traceamount that does not affect glass formation, which also applies to thefollowing discussion). Glass compositions having such a constitutionenable prevention of beforehand damages to a circuit due to migration ofalkali metal ions after a ceramic substrate circuit board has beensubjected to glass coating. Therefore, circuit boards or the like thathave been subjected to glass coating can be made more reliable anddurable.

Furthermore, the present invention can provide glaze forming pastes orother glass forming materials containing the glass compositions of thepresent invention as a primary component for glass formation.

For example, glass forming materials comprising a glass composition as aglass forming component are provided; the glass composition comprisesprimary oxide components in an amount of 85% or more (preferable 90% ormore) of the total weight of the composition; the primary oxidecomponents include ZnO, B₂O₃ and P₂O₅ as essential components and theprimary oxide components are provided in the amounts of 50 to 80% ofZnO, 5 to 35% of B₂O₃, 1 to 20% of P₂O₅, 0 to 10% of Al₂O₃, 0 to 15% ofMgO, 0 to 10% of CaO, and 0 to 5% of BaO. In the alternative, glassforming materials comprising a glass composition as a glass formingcomponent are provided, in which the glass composition is substantiallyfree of lead oxide and comprises primary oxide components in an amountof 90% or more (preferably 95% or more) of the total weight of thecomposition; the primary oxide components include ZnO, B₂O₃ and P₂O₅ asessential components and the primary oxide components are provided inthe amounts of 45 to 80% of ZnO (preferably 45 to 75% of ZnO), 5 to 45%of B₂O₃, 1 to 35% of P₂O₅, 0 to 10% of Al₂O₃, 0 to 15% of MgO, 0 to 10%of CaO, and 0 to 5% of BaO. These glass forming materials enable sealingand coating processes at firing temperatures that are lower than glassforming materials comprising the known lead-free glass composition asthe primary component.

Preferred glass forming materials comprise the glass composition in theform of a powder and an appropriate vehicle and are prepared as a paste.Such paste-like materials are suitable for forming a glass layer (glaze)on the surface of various ceramic products (substrates, etc.).

BEST MODES FOR PRACTICING THE INVENTION

Hereinafter, preferred embodiments of glass compositions of the presentinvention will be described. The percent representation (%) in thefollowing description refers to % by weight.

First, components of the glass composition of the present invention willbe described. The above-mentioned primary oxide components include ZnO,B₂O₃ and P₂O₅ as essential components. In addition to these oxides, atleast one oxide selected from Al₂O₃, MgO, CaO and BaO can be included asan optional component. Thus, the primary oxide components contained inthe glass component of the present invention may consist of only thethree essential components, ZnO, B₂O₃ and P₂O₅. In the alternative, thecomposition itself may be composed substantially of only these threeoxides.

ZnO is a primary constituent of the glass compositions of the presentinvention and the largest constituent of the primary oxide components.The glass compositions of the present invention enable stable glassformation by appropriately mixing ZnO and the following oxides. However,if the amount of ZnO is more than 80% or less than 45% of the totalprimary oxide components, devitrification tends to occur during glassformation in a cooling process; thus, these amounts are not preferable.Preferably, the weight percentage of ZnO to the total composition is 45%to 75%, and particularly preferably is 50% to 65%.

B₂O₃ is an oxide that is directly involved in glass formation. If theamount of B₂O₃ is less than 5% of the total primary oxide components,stable glass formation cannot be achieved. On the other hand, if theamount of B₂O₃ is more than 45% of the total primary oxide components,the softening temperature may be increased. In addition, devitrification(crystal precipitation) tends to occur during glass formation in acooling process; thus, these amounts are not preferable. This phenomenoncan adversely affect sealing or glass coating. Preferably, the weightpercentage of B₂O₃ to the total primary oxide components is 10% to 30%,and particularly preferably is 15% to 30%.

The oxides P₂O₅ and B₂O₃ are each directly involved in glass formation.P₂O₅ contributes to a reduction of the softening temperature. Additionof P₂O₅ can improve the smoothness of the glass surface. However, if theamount of P₂O₅ is more than 35% of the total primary oxide components,crystallization tends to occur during remelting; thus, the surfacesmoothness that is desired for sealing or coating applications may notbe achieved. Preferably, the weight percentage of P₂O₅ to the totalprimary oxide components is 10% to 30%, and particularly preferably is10% to 25%.

Al₂O₃, MgO, CaO and BaO are optional components that can be included inthe glass compositions of the present invention together with theprimary oxide components. If one or two or more of these oxides aremixed in appropriate amounts, crystallization may be suppressed, whichcrystallization can occur during remelting of the glass compositions.However, if the amount of either one of Al₂O₃ and CaO is more than 10%of the total primary oxide components, the amount of MgO is more than15% of the total primary oxide components, or the amount of BaO is morethan 5% of the total primary oxide components, then devitrificationtends to occur during glass formation in a cooling process or a similarprocess; thus, these amounts are not preferable.

The sum of the weight percentages of Al₂O₃, MgO, CaO and BaO ispreferably 15% or less of the total primary oxide components (providedthat the percentage of BaO is not more than 5%).

SiO₂ is a common oxide for forming glass, but is an unnecessaryconstituent for formulating the glass compositions of the presentinvention. If the amount of SiO₂ is more than 1% of the total glasscomposition, devitrification tends to occur during glass formation in acooling process. Moreover, the softening temperature may be too high;thus, this amount is not preferable. Therefore, the weight percentage ofSiO₂ with respect to the total composition is preferably less than 1%,and it is particularly preferable that SiO₂ is substantially notpresent.

Glass compositions of the present invention are defined by including anappropriate combination of the primary oxide components at a suitableformulation ratio of the above-described oxides in an amount of 85% ormore or 90% or more, preferably 95% or more, of the total composition.In the alternative, glass compositions of the present invention aredefined by being composed exclusively of some of the above-describedoxides with the exception of unavoidable impurities.

If glass compositions of the present invention are used as a coatingmaterial for glass-coating a ceramic material, a metal material or acomposite of a ceramic and a metal such as a ceramic circuit board, as asealing material for sealing these materials, or as a glaze (enamel),the primary oxide components having the following formulation ratiopreferably are provided in amount of 85% or more (preferably 90% ormore, more preferably 95% or more, and particularly preferably 100%) ofthe total composition. More specifically, the primary oxide componentsof the glass compositions of the present invention, which areparticularly preferable for the above-described applications, includeZnO, which accounts for 50 to 65% of the total primary oxide components,B₂O₃ and P₂O₅, which account for 30 to 45% (B₂O₃ is in the range from 10to 30% of the total primary oxide components, and P₂O₅ is in the rangefrom 10 to 30% of the total primary oxide components), and at least oneoxide selected from Al₂O₃, MgO, CaO and BaO, which accounts for 0 to 15%(BaO is selected such that the ratio is 0 to 5% of the total primaryoxide components). According to the above formulation ratios, Al₂O₃,MgO, CaO and BaO are not essential components, and the content of theseoxides can be 0%.

Glass compositions of the present invention are preferably comprise onlythe primary oxide components having the above-described formulations,but can include components other than the primary oxide components, aslong as the additional components do not affect the desired glassformation properties. For example, other compounds (e.g., oxides otherthan the oxides constituting the primary oxide components) that are notconstituents of the primary oxide components can be appropriately mixed.

The glass transition points (° C.) of the glass compositions of thepresent invention are generally in the range of 500° C. to 580° C. andtypically in the range of 520° C. to 560° C. The yield (deformation)points (° C.) of the glass compositions of the present invention aregenerally in the range of 520° C. to 680° C. and typically in the rangeof 540° C. to 580° C. Thus, glass compositions of the present inventionprovide the low temperature melting properties, i.e., low meltingpoints, which are preferable for sealing and coating (glaze formation).Therefore, the firing process can be performed at a lower firingtemperature than the known high PbO glass compositions (e.g.,compositions for forming borosilicate-lead glass). Typically, the firingprocess is performed for 10 to 20 min at a firing temperature of 700° C.or less (preferably 650° C. or less, typically 600 to 650° C.) in orderto seal or coat a ceramic material or a metal material. Thus, it ispossible to prevent degradation of the properties of the object thatwill be sealed or coated, which degradation would be caused by hightemperatures during the firing process. In addition, the effects ofmigration can be avoided by using glass compositions of the presentinvention that are substantially free of alkali metal oxides and alkalimetal ions. Thus, glass compositions of the present invention may besuitably used as glass forming materials for coating a surface (circuit)of a ceramic substrate.

Glass compositions of the present invention typically possess an averagethermal expansion coefficient between room temperature and 300° C.within the range of 4.5×10⁻⁶/° C. to 8.0×10⁻⁶/° C., and preferably5.0×10⁻⁶/° C. to 7.5×10⁻⁶/° C. The thermal expansion coefficient of theglass forming material can be adjusted by appropriately mixing in a lowexpansion material as a filler, which will be further described below.In addition to using the glass compositions of the present invention forcoating, as was described above, the glass composition also may be used,e.g., for decorating various glass products or attaching (joining)ceramic materials, metal materials or these materials.

There are no restrictions concerning methods for producing the glasscompositions of the present invention, and similar methods for producingknown glass compositions can be used. Typically, compounds that providethe oxides constituting the above primary oxide components and otheradditives are mixed in appropriate amounts to prepare a startingmaterial; the starting material is then heated and melted at a suitablyhigh temperature (typically, 1000° C. to 1500° C.). Thereafter, themolten product is cooled (preferably rapid cooled) to form a glass. Theresulting vitreous composition can be shaped into desired forms byvarious methods. For example, a powdered glass composition having adesired average particle size (e.g., 1 μm to 10 μm) can be obtained bygrinding with a ball mill.

If the glass compositions of the present invention are used as a glassforming material, generally speaking, the glass composition is preparedin the form of a powder, and the powdered composition is mixed withwater or an organic solvent to form a paste. For example, if the glasscompositions of the present invention are used as a glass formingcomponent of a paste-like glass forming material for glaze formation,the glass composition, which has been ground into a powder by milling orthe like, is typically mixed with a vehicle containing water or anorganic solvent in order to prepare the paste-like glass formingmaterial. Furthermore, various additives (fillers) can be added,depending upon the application and purpose. If a paste-like glassforming material is prepared, e.g., for forming a glaze on a ceramicsubstrate, a suitable solvent containing a suitable high molecularweight component dissolved therein can be used as the vehicle, althoughthe vehicle is not limited thereto. Examples of such suitable highmolecular weight components include, but are not limited to, variouscelluloses (methyl cellulose, ethyl cellulose, cellulose nitrate, etc.),acrylic resin, and epoxy resin. Examples of suitable solvents include,but are not limited to, ester solvents, such as butyl carbitol acetate,ether solvents, such as butyl cellosolve and butyl carbitol, organicsolvents, such as pine oil, various glycols and water. The ratio of thepowdered materials (including the powdered glass composition and variousadditives) that is mixed with the vehicle can be a matter of choice forthose skilled in the art and can be suitably determined in view of workefficiency. For example, 25 to 75 parts by weight of water or an organicsolvent may be mixed with 100 parts by weight of the powdered materialin order to prepare a paste.

An appropriate amount of the resulting glass forming material is appliedor sprayed onto a ceramic, such as alumina, or a metal object that willbe sealed or coated; then, a firing process is performed at a suitabletemperature, thereby obtaining the desired sealed product or glasscoated product.

Various additives (fillers) can be mixed with the glass compositions ofthe present invention during the preparation of the above-describedpaste-like glass forming material or other glass forming materials thatcan be provided by the present invention. Typical examples thereofinclude a variety of low expansion inorganic materials that can adjustthe thermal expansion coefficient of the glass compositions of thepresent invention, which is the primary component. For example, alumina,cordierite, zircon, β-eucryptite, forsterite, spodumene, quartz glass,aluminum titanate, or the like can be used as low expansion inorganicmaterials. In particular, alumina is the most preferred for adjustingthe thermal expansion coefficient among the above-listed low expansioninorganic materials. The low expansion inorganic material is mixed withthe glass composition of the present invention such that the amount ofthe low expansion inorganic material is 20% or less (preferably 10% orless) of the total glass forming material. If a greater amount of filleris added, a relatively insufficient amount of the glass formingcomponent is provided, which is not preferable. If, e.g., the glassforming component is insufficient, the airtightness of the sealedportion may be insufficient when the glass forming component is used forsealing.

Similar to the preparation of the paste, a typical method for preparingthe glass forming material containing such a filler is to provide thefiller as a powder; then, the powdered filler is mixed in a suitableratio with the glass composition of the present invention, which hasalso been ground into a powder.

The present invention will be described in greater detail by way of thefollowing examples. The present invention is not limited to theseexamples.

Glass compositions of the present invention having the compositionsshown in Table 1 (Examples 1 to 9), a glass forming material containinga glass composition of the present invention (Example 10) and a knownhigh PbO glass composition, which serves as a comparative example(Comparative Example 1), were prepared.

More specifically, in order to prepare compositions having theformulations (wt %) shown in Table 1, raw materials were suitablyselected from H₃BO₃, P₂O₅, Zn₃(PO₄)₂4H₂O, ZnO, Al₂O₃, magnesiumcarbonate hydroxide, CaCO₃, BaCO₃, SiO₂, PbO, Fe₂O₃ or the like, wereweighed such that a predetermined mixing ratio was obtained and werethen mixed using a mixer. The resulting product was placed in a platinumpot and melted at a suitably high temperature (herein, 1200° C.) in anelectrical furnace. Then, the molten product was removed from thefurnace and was brought into contact with a low temperature element(herein, poured onto a stainless steel plate) for rapid cooling in orderto form a glass having a predetermined shape (herein, plate-like). Then,the resulting plate-like glass was ground using a ball mill in order toprepare powdered glass compositions of the present invention and apowdered high PbO glass composition (Examples 1 to 9 and ComparativeExample 1). Furthermore, in Example 10, powdered alumina was added andmixed with the prepared powdered glass composition in order to providethe formulation ratio shown in Table 1; thus, a glass forming materialwas obtained that substantially comprised the glass composition of thepresent invention and alumina (filler).

Then, the glass transition point, the yield point and the averagethermal expansion coefficient were measured as indexes indicating theproperties of the resulting glass compositions and glass formingmaterials.

More specifically, the powdered products of each example and thecomparative example were compressed into predetermined forms and firedat 600° C. for 20 minutes, thereby producing rod-shaped samples having alength of 20 mm and a diameter of 4 mm. Then, the glass transition point(° C.), the yield point (° C.) and the average thermal expansioncoefficient from room temperature to 400° C. or 500° C. were measuredusing a thermo-mechanical analyzer (TMA) or a differential thermal(expansion) analyzer. Table 1 shows the results.

TABLE 1 Ex. Comp. Ex. 1 2 3 4 5 6 7 8 9 10 1 Composition Composition (wt%) (wt %) B₂O₃ 18.1 27.3 17.0 16.2 17.4 15.7 16.3 17.3 13.2 16.5 SiO₂15.2 P₂O₅ 20.6 11.0 19.4 18.5 19.2 17.3 18.5 19.2 26.1 18.8 B₂O₃ 17.3ZnO 61.2 61.6 58.3 55.8 58.4 53.3 56.0 58.7 60.7 55.7 PbO 54.4 Al₂O₃ 0.10.1 5.2 9.5 Al₂O₃ 2.5 MgO 5.0 13.7 Fe₂O₃ 0.5 CaO 0.1 9.2 BaO 4.8 SiO₂0.1 Alumina 9.0 Alumina 10.0 (Filler) (Filler) Glass 520 538 533 542 535550 521 530 560 528 Glass 470 Transition Transition Point (° C.) Point(° C.) Yield Point 550 566 558 574 566 572 544 553 670 561 Yield Point500 (° C.) (° C.) Thermal 6.2 5.9 6.1 5.4 7.1 7.4 7.1 6.2 5.2 6.5Thermal 8.5 Expansion Expansion Coefficient Coefficient (×10⁻⁶/° C.)(×10⁻⁶/° C.)

As can be seen from the property data shown in Table 1, if the glasscompositions and the glass forming materials of the examples are used,the sealing or coating process can be performed within a comparativelylow temperature range of 700° C. or less (typically 650° C. or less),similar to known high PbO glass compositions. Furthermore, as can beseen from the results of the measured average thermal expansioncoefficients, the glass compositions and the glass forming materials ofthe examples preferably can be used for coating a ceramic substrate madeof alumina or the like.

Furthermore, a glaze forming paste was prepared using the powdered glasscompositions of Examples 1 to 9. More specifically, 25 parts by weightof an organic solvent (butyl cellosolve acetate) containing an ethylcellulose binder and 75 parts by weight of the powdered glasscomposition were mixed in order to prepare pastes containing each of therespective glass compositions of Examples 1 to 9 as the primarycomponent. Then, these pastes were screen-printed on the surface of analumina substrate and were fired at a temperature of 600 to 700° C.,thereby forming a striped glaze (thickness of 20 μm) on the aluminasubstrate. In all the samples, the resulting glaze presented a smoothand glossy surface.

Although detailed examples of the present invention have been described,these examples are merely illustrative and can be practiced with avariety of changes and modifications that may be made using theknowledge of those skilled in the art.

As can be seen from the above-described examples, according to the glasscompositions of the present invention, glass forming materials can beprepared that are functionally comparable to, and can replace, high PbOglass compositions. In other words, according to the glass compositionsof the present invention and the glass forming materials (glaze formingpastes or the like) containing the composition as a vitreous component(glass forming component), glass coating processes for a ceramicsubstrate or the like or sealing processes can be performed atcomparatively low firing temperatures, similar to known high PbO glasscompositions.

What is claimed is:
 1. A composition of matter, comprising; an inorganicmaterial and a glass composition forming a coating on the inorganicmaterial, the glass composition comprising: ZnO in an amount of 50-80%by weight, B₂O₃ in an amount of 5-35% by weight, P₂O₅ in an amount of1-20% by weight, Al₂O₃ in an amount of 0-10% by weight, MgO in an amountof 0-15% by weight, CaO in an amount of 0-10% by weight, and BaO in anamount of 0-5% by weight, wherein said oxides comprise at least 85% ofthe total weight of the glass composition and the glass composition issubstantially free of alkali metal oxides and alkali metal ions.
 2. Acomposition of matter as in claim 1, wherein the glass compositioncomprises SiO₂ in an amount of less than 1% of the total weight of theglass composition.
 3. A composition of matter as in claim 2, wherein theglass composition is substantially free of SiO₂.
 4. A composition ofmatter as in claim 3, wherein the glass composition essentially consistsof said oxides.
 5. A composition of matter, comprising: an inorganicmaterial and a glass composition forming a coating on the inorganicmaterial, the glass composition comprising: ZnO in an amount of 45-80%by weight, B₂O₃ in an amount of 5-45% by weight, P₂O₅ in an amount of1-35% by weight, Al₂O₃ in an amount of 0-10% by weight, MgO in an amountof 0-15% by weight, CaO in an amount of 0-10% by weight, and BaO in anamount of 0-5% by weight, wherein said oxides comprise at least 90% ofthe total weight of the glass composition and wherein the glasscomposition is substantially free of alkali metal oxides, alkali metalions and lead oxides.
 6. A composition of matter as in claim 5, whereinthe glass composition comprises: ZnO in an amount of 50-65% by weight,B₂O₃ in an amount of 10-30% by weight, P₂O₅ in an amount of 10-30% byweight, wherein the sum of the weight percentages of B₂O₃ and P₂O₅ is30-45% of the total weight of said oxides, and at least one oxideselected from the group consisting of Al₂O₃, MgO, CaO and BaO in anamount of 0 to 15% by weight, wherein the weight percentage of BaO is0-5% of the total weight of said oxides.
 7. A composition of matter asin claim 6, wherein the glass composition comprises SiO₂ in an amount ofless than 1% of the total weight of the glass composition.
 8. Acomposition of matter as in claim 7, wherein the glass composition issubstantially free of SiO₂.
 9. A composition of matter as in claim 8,wherein the glass composition essentially consists of said oxides.
 10. Acoating material, comprising: a glass composition in the form of apowder, the glass composition comprising: ZnO in an amount of 50-80% byweight, B₂O₃ in an amount of 5-35% by weight, P₂O₅ in an amount of 1-20%by weight, Al₂O₃ in an amount of 0-10% by weight, MgO in an amount of0-15% by weight, CaO in an amount of 0-10% by weight, and BaO in anamount of 0-5% by weight, wherein said oxides comprise at least 85% ofthe total weight of the glass composition and the glass composition issubstantially free of alkali metal oxides and alkali metal ions, and avehicle, wherein the powderized glass composition is suspended in thevehicle and the coating material is in the form of a paste.
 11. Acoating material as in claim 10, wherein the glass compositionessentially consists of said oxides.
 12. A coating material, comprising:a glass composition in the form of a powder, the glass compositioncomprising: ZnO in an amount of 45-80% by weight, B₂O₃ in an amount of5-45% by weight, P₂O₅ in an amount of 1-35% by weight, Al₂O₃ in anamount of 0-10% by weight, MgO in an amount of 0-15% by weight, CaO inan amount of 0-10% by weight, and BaO in an amount of 0-5% by weight,wherein said oxides comprise at least 90% of the total weight of theglass composition and wherein the glass composition is substantiallyfree of alkali metal oxides, alkali metal ions and lead oxides, and avehicle, wherein the powderized glass composition is suspended in thevehicle and the coating material is in the form of a paste.
 13. Acoating material as in claim 12, wherein the glass compositioncomprises: ZnO in an amount of 50-65% by weight, B₂O₃ in an amount of10-30% by weight, P₂O₅ in an amount of 10-30% by weight, wherein the sumof the weight percentages of B₂O₃ and P₂O₅ is 30-45% of the total weightof said oxides, and at least one oxide selected from the groupconsisting of Al₂O₃, MgO, CaO, and BaO in an amount of 0 to 15% byweight, wherein the weight percentage of BaO is 0-5% of the total weightof said oxides.
 14. A coating material as in claim 13, wherein the glasscomposition essentially consists oxides.
 15. A method for forming aglass layer on a surface of an inorganic material, comprising: applyinga coating material to the surface of the inorganic material, and firingthe coating material and the inorganic material, thereby forming theglass layer, wherein the coating material comprises: a glass compositionin the form of a powder, the glass composition comprising: ZnO in anamount of 50-80% by weight, B₂O₃ in an amount of 5-35% by weight, P₂O₅in an amount of 1-20% by weight, Al₂O₃ in an amount of 0-10% by weight,MgO in an amount of 0-15% by weight, CaO in an amount of 0-10% byweight, and BaO in an amount of 0-5% by weight, wherein said oxidescomprise at least 85% of the total weight of the glass composition andthe glass composition is substantially free of alkali metal oxides andalkali metal ions, and a vehicle, wherein the powderized glasscomposition is suspended in the vehicle and the coating material is inthe form of a paste.
 16. A method as in claim 15, wherein the inorganicmaterial is selected from a ceramic material, a metal material, a glassproduct or a composite of a ceramic and a metal.
 17. A method as inclaim 15, wherein the inorganic material is a ceramic material.
 18. Amethod for forming a glass layer on a surface of an inorganic material,comprising: applying a coating material to the surface of the inorganicmaterial, and firing the coating material and the inorganic material,thereby forming the glass layer, wherein the coating material comprises:a glass composition in the form of a powder, the glass compositioncomprising: ZnO in an amount of 50-80% by weight, B₂O₃ in an amount of5-35% by weight, P₂O₅ in an amount of 1-20% by weight, Al₂O₃ in anamount of 0-10% by weight, MgO in an amount of 0-15% by weight, CaO inan amount of 0-10% by weight, and BaO in an amount of 0-5% by weight,wherein said oxides comprise at least 85% of the total weight of theglass composition and the glass composition is substantially free ofalkali metal oxides and alkali metal ions, and a vehicle, wherein thepowderized glass composition is suspended in the vehicle and the coatingmaterial is in the form of a paste, and wherein the glass compositionessentially consists of said oxides.
 19. A method for forming a glasslayer on a surface of an inorganic material, comprising: applying acoating material to the surface of the inorganic material, and firingthe coating material and the inorganic material, thereby forming theglass layer, wherein the coating material comprises: a glass compositionin the form of a powder, the glass composition comprising: ZnO in anamount of 45-80% by weight, B₂O₃ in an amount of 5-45% by weight, P₂O₅in an amount of 1-35% by weight, Al₂O₃ in an amount of 0-10% by weight,MgO in an amount of 0-15% by weight, CaO in an amount of 0-10% byweight, and BaO in an amount of 0-5% by weight, wherein said oxidescomprise at least 90% of the total weight of the glass composition andwherein the glass composition is substantially free of alkali metaloxides, alkali metal ions and lead oxides, and a vehicle, wherein thepowderized glass composition is suspended in the vehicle and the coatingmaterial is in the form of a paste.
 20. A method for forming a glasslayer on a surface of an inorganic material, comprising: applying acoating material to the surface of the inorganic material, and firingthe coating material and the inorganic material, thereby forming theglass layer, wherein the coating material comprises: a glass compositionin the form of a powder, the glass composition comprising: ZnO in anamount of 45-80% by weight, B₂O₃ in an amount of 5-45% by weight, P₂O₅in an amount of 1-35% by weight, Al₂O₃ in an amount of 0-10% by weight,MgO in an amount of 0-15% by weight, CaO in an amount of 0-10% byweight, and BaO in an amount of 0-5% by weight, wherein said oxidescomprise at least 90% of the total weight of the glass composition andwherein the glass composition is substantially free of alkali metaloxides, alkali metal ions and lead oxides, and a vehicle, wherein thepowderized glass composition is suspended in the vehicle and the coatingmaterial is in the form of a paste, wherein the glass compositionfurther comprises: ZnO in an amount of 50-65% by weight, B₂O₃ in anamount of 10-30% by weight, P₂O₅ in an amount of 10-30% by weight,wherein the sum of the weight percentages of B₂O₃ and P₂O₅ is 30-45% ofthe total weight of said oxides, and at least one oxide selected fromthe group consisting of Al₂O₃, MgO, CaO, and BaO in an amount of 0 to15% by weight, wherein the weight percentage of BaO is 0-5% of the totalweight of said oxides.
 21. A method for forming a glass layer on asurface of an inorganic material, comprising: applying a coatingmaterial to the surface of the inorganic material, and firing thecoating material and the inorganic material, thereby forming the glasslayer, wherein the coating material comprises: a glass composition inthe form of a powder, the glass composition comprising: ZnO in an amountof 45-80% by weight, B₂O₃ in an amount of 5-45% by weight, P₂O₅ in anamount of 1-35% by weight, Al₂O₃ in an amount of 0-10% by weight, MgO inan amount of 0-15% by weight, CaO in an amount of 0-10% by weight, andBaO in an amount of 0-5% by weight, wherein said oxides comprise atleast 90% of the total weight of the glass composition and wherein theglass composition is substantially free of alkali metal oxides, alkalimetal ions and lead oxides, and a vehicle, wherein the powderized glasscomposition is suspended in the vehicle and the coating material is inthe form of a paste, wherein the glass composition further comprises:ZnO in an amount of 50-65% by weight, B₂O₃ in an amount of 10-30% byweight, P₂O₅ in an amount of 10-30% by weight, wherein the sum of theweight percentages of B₂O₃ and P₂O₅ is 30-45% of the total weight ofsaid oxides, and at least one oxide selected from the group consistingof Al₂O₃, MgO, CaO, and BaO in an amount of 0 to 15% by weight, whereinthe weight percentage of BaO is 0-5% of the total weight of said oxides,wherein the glass composition essentially consists of said oxides.
 22. Amethod as in claim 21, wherein the inorganic material is selected from aceramic material, a metal material, a glass product or a composite of aceramic and a metal.
 23. A method as in claim 21, wherein the inorganicmaterial is a ceramic material.